The present invention relates to a process for the production of hexachlorocyclobutene from technical hexachlorobutadiene by cyclization of the hexachlorobutadiene to hexachlorocyclobutene and separation of the hexachlorocyclobutene by means of rectification.
Hexachlorobutadiene can be produced as a coproduct with carbon tetrachloride in the manufacture of perchloroethylene as disclosed in Kirk-Othmer, "Encyclopedia of Chemical Technology", Volume 5, (1964) under the section "Carbon Tetrachloride" particularly pages 132 and 133, the disclosure of which is incorporated herein.
The technical hexachlorobutadeiene preferably used as the raw material in the present invention has a hexachlorobutadiene concentration of about 98 to 100 percent by weight and hexachlorocyclobutene concentration of about 0 to 2 percent by weight. This technical hexachlorobutadiene is prepared as disclosed in U.S. Pat. No. 2 960 543 or Japanese Pat. No. 73 42615 (examinated application).
Hexachlorocyclobutene is an interesting intermediate product for the synthesis of organic compounds. This compound is obtained in the laboratory by reacting hexafluorocyclobutene with aluminum chloride. From technical hexachlorobutadiene, hexachlorocyclobutene can be enriched up to approximately 20% by vacuum fractionation and low-temperature crystallization ("Angew. Chemie"[Applied Chemistry] 78 [1966] p. 928, last paragraph, to page 929, third paragraph). It is furthermore known that hexafluoro-and hexachlorobutadiene can be arranged in an equilibrium reaction into hexafluoro-and hexachlorocyclobutene, respectively. In the case of the hexafluoro derivative, the cyclic structure is more stable from a thermodynamic viewpoint, while the openchain structure is greatly preferred in the case of hexachlorobutadiene ("Angew. Chemie") 78 [1966]p. 928, last paragraph, to p. 929, second paragraph). In accordance with this publication, a cyclization of the hexachlorobutadiene to hexachlorocyclobutene was to be just as unsuitable as a purification by means of distillation, since a 20% enrichment is completely insufficient from a commercial viewpoint.